Wireless networks that link together multiple computers are commonplace and the technology for implementing such networks is rapidly growing. The common names for such networking technology are “wireless networking”, “WiFi” or “802.11 networking.” The big advantage of wireless networking is simplicity, because it allows computers to be connected anywhere in a home or office without the need for physical wires, thereby allowing the computers to be mobile. The computers, called “wireless clients”, connect to the network using broadcast radio signals which can travel up to distances of approximately 100 feet.
Wireless networks are generally governed by one of several standards promulgated by the Institute of Electrical and Electronics Engineers (IEEE). The basic standard is denoted as the 802.11 standard and covers wireless networks. The standard has several different versions labeled by a, b and g notations. The different standard versions differ in several respects, including the broadcast signal frequency, transmission speed and data coding techniques. For example, the first wireless networking systems to reach the marketplace were constructed according to the 802.11b standard. Equipment that conforms to the 802.11b standard transmits at 2.4 GHz, can handle data transmission speeds up to 11 megabits per second and uses a data coding technique called “complementary code keying”. The 802.11a standard next appeared. Equipment conforming to this standard operates at 5 GHz, can handle up to 54 megabits per second and uses a data coding technique called “orthogonal frequency-division multiplexing” (OFDM). The 802.11g standard has characteristics of both the 802.11a and 802.11b standards in that conforming equipment operates at 2.4 Ghz, but has data transmission speeds of 54 megabits per second and uses OFDM encoding.
Wireless communications are usually designed to take place in a localized area quite often via a local communications network. Such a localized area may be a building, an area within a building, an area comprising several buildings, outdoor areas, or a combination of indoor and outdoor areas. However, due to the broadcast nature of the radio-frequency signal, persons outside of the localized area can often receive the signal and, thus, communicate with the network. In many environments, information on the network is confidential and the ability of unauthorized persons to attach to the network is a serious problem.
A common technique for enhancing the security of a wireless network is to encode the information broadcast via the radio-frequency signals with a WEP key. WEP stands for “Wired Equivalent Privacy”, and is an encryption standard that is part of the 802.11 standard. Another technique is to track the physical location of the mobile equipment and disconnect it from the network if the equipment strays outside of a predetermined localized area.
The communication between mobile wireless devices and the local area network (LAN) is often performed using devices, such as “access points” (APs) that are attached to the LAN. The APs are communication ports for wireless devices, which broadcast the radio-frequency signals to, and receive the radio-frequency signals from, the wireless clients. The APs pass messages received from the wireless device across the LAN to other servers, computers, applications, subsystems or systems, as appropriate. Typically, the APs are coupled to one or more network servers, which manage the message traffic flow. Application servers may be coupled to or accessed via the network servers, to provide data or typical application functionality to the wireless device.
Detection and location within a defined local area is often performed using a LAN to which a set of sensors is attached. In order to use such a local area network to determine the physical location of a wireless client, the local area network is equipped with a plurality of radio-frequency signal sensors, which may be incorporated into the access points or may be separate from the access points. Using a technique called “RF fingerprinting” a digital definition of the physical localized area is first developed and then a statistical signal strength model is developed to provide a context within which the detection and tracking will occur. Then the actual radio-frequency signal strength as measured at the sensors is compared to the model to calculate the physical location of each device.
The digital definition of the localized area is comprised of a set of defined regions, areas or locations (collectively referred to as “locales”) taking into account various obstructions. Once the digital form of the localized area is formed, the locales are defined and the statistical signal strength model is then defined.
With the digital form of the physical space defined, the signal strength model can be determined. The signal strength model defines, for each access point within the localized area, a pattern of signal strength reception that is anticipated from a mobile device transmitting within the area, taking into account the obstructions and placement of the access points. The signal strength model can be created by actually installing sensors in the physical space and then measuring the strength of signals received at the sensors as a transmitting wireless client moves through the area. Alternatively, simulated access points and simulated wireless client readings can be used to generate the signals strength model.
After the signal strength model is determined, the location of a wireless client can be determined by collecting actual signal strength data from the device as it moves about or resides in the localized area and comparing the actual data against values predicted by the signal strength model. The RF fingerprinting process is described in more detail in U.S. Pat. No. 6,674,403, the contents of which are hereby incorporated in their entirety by reference.
Alternatively, other location techniques could be used. For example, some known location techniques use the time of arrival of signals or differences between the time of arrival of signals from the wireless device at the APs to calculate the location of the wireless device. For example, such systems are described in U.S. Pat. Nos. 6,801,782 and 6,756,940.
Once a wireless client has been located, access is usually denied if the unit is outside the localized area. This provides security and prevents unauthorized users from attaching or staying attached to the network, but is not very flexible because the system cannot differentiate between authorized users who are properly attached to the network.